Perform a block on a sequential number of objects in an array forwards or backwards.

main.m

#import <Foundation/Foundation.h>


int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // Setup a test array
    NSArray *test = [NSArray arrayWithObjects:@"Object 1", @"Object 2", @"Object 3", @"Object 4", @"Object 5", nil];

    // Test 1 - run through the first 3 items
    NSLog(@"<<<<<<Test 1>>>>>>");
    [test dsl_enumerateUpTo:3 inDirection:DSLEnumerationForward usingBlock:^(id theObject, NSUInteger idx, BOOL *stop) {
        NSLog(@"%@", theObject);
    }];
    
    // Test 2 - run through the first 3 items backwards
    NSLog(@"<<<<<<Test 2>>>>>>");
    [test dsl_enumerateUpTo:3 inDirection:DSLEnumerationReverse usingBlock:^(id theObject, NSUInteger idx, BOOL *stop) {
        NSLog(@"%@", theObject);
    }];

    // Test 3 - run through the first 3 items forwards, but stop on "Object 2"
    NSLog(@"<<<<<<Test 3>>>>>>");
    [test dsl_enumerateUpTo:3 inDirection:DSLEnumerationForward usingBlock:^(id theObject, NSUInteger idx, BOOL *stop) {
        NSString *testString = @"Object 2";
        
        NSLog(@"%@", theObject);
        
        if ([theObject isEqualToString:testString]) {
            NSLog(@"Test string found: %@", testString);
            *stop = YES;
        }
    }];
    
    // Test 4 - run through the first 3 items backwards, but stop on "Object 4"
    NSLog(@"<<<<<<Test 4>>>>>>");
    [test dsl_enumerateUpTo:3 inDirection:DSLEnumerationReverse usingBlock:^(id theObject, NSUInteger idx, BOOL *stop) {
        NSString *testString = @"Object 4";
        
        NSLog(@"%@", theObject);
        
        if ([theObject isEqualToString:testString]) {
            NSLog(@"Test string found: %@", testString);
            *stop = YES;
        }
    }];
    
    [pool drain];
    return 0;
}

NSArray+DSLFirstItems.h

//
//  NSArray+DSLFirstItems.h
//
//  Created by Pete Callaway on 15/10/2010.
//  Copyright 2010 Dative Studios. All rights reserved.
//  Modified by Abizer Nasir
//

#import <Foundation/Foundation.h>

enum _DSLEnumerationOption {
    DSLEnumerationForward = 0,
    DSLEnumerationReverse = 1
};
typedef NSUInteger DSLEnumerationOption;


@interface NSArray (DSLFirstItems)

- (void)dsl_enumerateUpTo:(NSUInteger)numberOfItemsToEnumerate inDirection:(DSLEnumerationOption)direction usingBlock:(void (^)(id object, NSUInteger idx, BOOL *stop))block;

@end

NSArray+DSLFirstItems.m

//
//  NSArray+DSLFirstItems.m
//
//  Created by Pete Callaway on 15/10/2010.
//  Copyright 2010 Dative Studios. All rights reserved.
//  Modified by Abizer Nasir
//

#import "NSArray+DSLFirstItems.h"


@implementation NSArray (DSLFirstItems)

- (void)dsl_enumerateUpTo:(NSUInteger)numberOfItemsToEnumerate inDirection:(DSLEnumerationOption)direction usingBlock:(void (^)(id object, NSUInteger idx, BOOL *stop))block {
    NSInteger count = 0;
    BOOL stop = NO;
    
    id <NSFastEnumeration> iterable;
    
    if (direction == DSLEnumerationForward) {
        iterable = self;
    } else {
        iterable = [self reverseObjectEnumerator];
    }

    for (id object in iterable) {
        block(object, count, &stop);
        
        if (stop) return;
        
        count++;
        if (count >= numberOfItemsToEnumerate) return;
    }
}

@end